Benefficient produced a gutsy performance to land the Jewson Novices' Chase, the opening event on the third day of the Cheltenham Festival.
Tony Martin's charge was allowed to go off a 20-1 shot in the hands of Bryan Cooper, but he made a mockery of his odds as he accounted for hot favourite Dynaste.
Benefficient had been prominent throughout, but his challenge looked to be over when he was headed some way from home. However, Cooper switched him back to challenge up the inside and he found a second wind to power up the hill and win by three and a quarter lengths.
Cooper said: "It's unbelievable, it's what you dream of as a young boy. Tony said to me that if he gets headed turning in, to just sit on him and let him fiddle away.
"Some of the others might have had more speed than him, but they couldn't get away from me. He winged the last and galloped all the way to the line."
Martin added: "This is what you get up every morning for, to come here with a live chance. I thought if everything went well he couldn't be out of the first three, but we were very much afraid of Dynaste. We knew he'd get two and a half miles, he got the run of the race and jumped excellent.
"The jockey was excellent. As far as I'm concerned Ruby Walsh, Barry Geraghty, Paul Carberry and Tony McCoy are out on their own, but they are the old guard, this boy is on the way up and he'll be there when they have long gone.
"He's a good moving horse and the better ground helped. Today was the plan."
Tom Scudamore, rider of Dynaste, said: "He's run a great race and he's the best of the English horses. He jumped fantastically and was beaten by a better horse on the day. It seems that the Irish staying novices are better this year."
A terse David Pipe, trainer of Dynaste, added: "Just not good enough. He might go to Aintree, but I'm happy we picked the right race."